arm64: mm: Introduce PTE_WRITE

We have the following means for encoding writable or dirty ptes:

                                PTE_DIRTY       PTE_RDONLY
!pte_dirty && !pte_write        0               1
!pte_dirty && pte_write         0               1
pte_dirty && !pte_write         1               1
pte_dirty && pte_write          1               0

So we can't distinguish between writable clean ptes and read only
ptes. This can cause problems with ptes being incorrectly flagged as
read only when they are writable but not dirty.

This patch introduces a new software bit PTE_WRITE which allows us to
correctly identify writable ptes. PTE_RDONLY is now only clear for
valid ptes where a page is both writable and dirty.

Signed-off-by: Steve Capper <steve.capper@arm.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

1 files changed, 25 insertions, 23 deletions

diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index 27c78395ae76..b524dcd17243 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -28,7 +28,7 @@
 #define PTE_FILE                (_AT(pteval_t, 1) << 2) /* only when !pte_present() */
 #define PTE_DIRTY               (_AT(pteval_t, 1) << 55)
 #define PTE_SPECIAL             (_AT(pteval_t, 1) << 56)
-                                /* bit 57 for PMD_SECT_SPLITTING */
+#define PTE_WRITE               (_AT(pteval_t, 1) << 57)
 #define PTE_PROT_NONE           (_AT(pteval_t, 1) << 58) /* only when !PTE_VALID */
 
 /*
@@ -67,15 +67,15 @@ extern pgprot_t pgprot_default;
 
 #define _MOD_PROT(p, b)         __pgprot_modify(p, 0, b)
 
-#define PAGE_NONE               __pgprot_modify(pgprot_default, PTE_TYPE_MASK, PTE_PROT_NONE | PTE_RDONLY | PTE_PXN | PTE_UXN)
-#define PAGE_SHARED             _MOD_PROT(pgprot_default, PTE_USER | PTE_NG | PTE_PXN | PTE_UXN)
-#define PAGE_SHARED_EXEC        _MOD_PROT(pgprot_default, PTE_USER | PTE_NG | PTE_PXN)
-#define PAGE_COPY               _MOD_PROT(pgprot_default, PTE_USER | PTE_NG | PTE_PXN | PTE_UXN | PTE_RDONLY)
-#define PAGE_COPY_EXEC          _MOD_PROT(pgprot_default, PTE_USER | PTE_NG | PTE_PXN | PTE_RDONLY)
-#define PAGE_READONLY           _MOD_PROT(pgprot_default, PTE_USER | PTE_NG | PTE_PXN | PTE_UXN | PTE_RDONLY)
-#define PAGE_READONLY_EXEC      _MOD_PROT(pgprot_default, PTE_USER | PTE_NG | PTE_PXN | PTE_RDONLY)
-#define PAGE_KERNEL             _MOD_PROT(pgprot_default, PTE_PXN | PTE_UXN | PTE_DIRTY)
-#define PAGE_KERNEL_EXEC        _MOD_PROT(pgprot_default, PTE_UXN | PTE_DIRTY)
+#define PAGE_NONE               __pgprot_modify(pgprot_default, PTE_TYPE_MASK, PTE_PROT_NONE | PTE_PXN | PTE_UXN)
+#define PAGE_SHARED             _MOD_PROT(pgprot_default, PTE_USER | PTE_NG | PTE_PXN | PTE_UXN | PTE_WRITE)
+#define PAGE_SHARED_EXEC        _MOD_PROT(pgprot_default, PTE_USER | PTE_NG | PTE_PXN | PTE_WRITE)
+#define PAGE_COPY               _MOD_PROT(pgprot_default, PTE_USER | PTE_NG | PTE_PXN | PTE_UXN)
+#define PAGE_COPY_EXEC          _MOD_PROT(pgprot_default, PTE_USER | PTE_NG | PTE_PXN)
+#define PAGE_READONLY           _MOD_PROT(pgprot_default, PTE_USER | PTE_NG | PTE_PXN | PTE_UXN)
+#define PAGE_READONLY_EXEC      _MOD_PROT(pgprot_default, PTE_USER | PTE_NG | PTE_PXN)
+#define PAGE_KERNEL             _MOD_PROT(pgprot_default, PTE_PXN | PTE_UXN | PTE_DIRTY | PTE_WRITE)
+#define PAGE_KERNEL_EXEC        _MOD_PROT(pgprot_default, PTE_UXN | PTE_DIRTY | PTE_WRITE)
 
 #define PAGE_HYP                _MOD_PROT(pgprot_default, PTE_HYP)
 #define PAGE_HYP_DEVICE         __pgprot(PROT_DEVICE_nGnRE | PTE_HYP)
@@ -83,13 +83,13 @@ extern pgprot_t pgprot_default;
 #define PAGE_S2                 __pgprot_modify(pgprot_default, PTE_S2_MEMATTR_MASK, PTE_S2_MEMATTR(MT_S2_NORMAL) | PTE_S2_RDONLY)
 #define PAGE_S2_DEVICE          __pgprot(PROT_DEFAULT | PTE_S2_MEMATTR(MT_S2_DEVICE_nGnRE) | PTE_S2_RDWR | PTE_UXN)
 
-#define __PAGE_NONE             __pgprot(((_PAGE_DEFAULT) & ~PTE_TYPE_MASK) | PTE_PROT_NONE | PTE_RDONLY | PTE_PXN | PTE_UXN)
-#define __PAGE_SHARED           __pgprot(_PAGE_DEFAULT | PTE_USER | PTE_NG | PTE_PXN | PTE_UXN)
-#define __PAGE_SHARED_EXEC      __pgprot(_PAGE_DEFAULT | PTE_USER | PTE_NG | PTE_PXN)
-#define __PAGE_COPY             __pgprot(_PAGE_DEFAULT | PTE_USER | PTE_NG | PTE_PXN | PTE_UXN | PTE_RDONLY)
-#define __PAGE_COPY_EXEC        __pgprot(_PAGE_DEFAULT | PTE_USER | PTE_NG | PTE_PXN | PTE_RDONLY)
-#define __PAGE_READONLY         __pgprot(_PAGE_DEFAULT | PTE_USER | PTE_NG | PTE_PXN | PTE_UXN | PTE_RDONLY)
-#define __PAGE_READONLY_EXEC    __pgprot(_PAGE_DEFAULT | PTE_USER | PTE_NG | PTE_PXN | PTE_RDONLY)
+#define __PAGE_NONE             __pgprot(((_PAGE_DEFAULT) & ~PTE_TYPE_MASK) | PTE_PROT_NONE | PTE_PXN | PTE_UXN)
+#define __PAGE_SHARED           __pgprot(_PAGE_DEFAULT | PTE_USER | PTE_NG | PTE_PXN | PTE_UXN | PTE_WRITE)
+#define __PAGE_SHARED_EXEC      __pgprot(_PAGE_DEFAULT | PTE_USER | PTE_NG | PTE_PXN | PTE_WRITE)
+#define __PAGE_COPY             __pgprot(_PAGE_DEFAULT | PTE_USER | PTE_NG | PTE_PXN | PTE_UXN)
+#define __PAGE_COPY_EXEC        __pgprot(_PAGE_DEFAULT | PTE_USER | PTE_NG | PTE_PXN)
+#define __PAGE_READONLY         __pgprot(_PAGE_DEFAULT | PTE_USER | PTE_NG | PTE_PXN | PTE_UXN)
+#define __PAGE_READONLY_EXEC    __pgprot(_PAGE_DEFAULT | PTE_USER | PTE_NG | PTE_PXN)
 
 #endif /* __ASSEMBLY__ */
 
@@ -140,7 +140,7 @@ extern struct page *empty_zero_page;
 #define pte_dirty(pte)          (pte_val(pte) & PTE_DIRTY)
 #define pte_young(pte)          (pte_val(pte) & PTE_AF)
 #define pte_special(pte)        (pte_val(pte) & PTE_SPECIAL)
-#define pte_write(pte)          (!(pte_val(pte) & PTE_RDONLY))
+#define pte_write(pte)          (pte_val(pte) & PTE_WRITE)
 #define pte_exec(pte)           (!(pte_val(pte) & PTE_UXN))
 
 #define pte_valid_user(pte) \
@@ -148,13 +148,13 @@ extern struct page *empty_zero_page;
 
 static inline pte_t pte_wrprotect(pte_t pte)
 {
-        pte_val(pte) |= PTE_RDONLY;
+        pte_val(pte) &= ~PTE_WRITE;
         return pte;
 }
 
 static inline pte_t pte_mkwrite(pte_t pte)
 {
-        pte_val(pte) &= ~PTE_RDONLY;
+        pte_val(pte) |= PTE_WRITE;
         return pte;
 }
 
@@ -201,8 +201,10 @@ static inline void set_pte_at(struct mm_struct *mm, unsigned long addr,
         if (pte_valid_user(pte)) {
                 if (pte_exec(pte))
                         __sync_icache_dcache(pte, addr);
-                if (!pte_dirty(pte))
-                        pte = pte_wrprotect(pte);
+                if (pte_dirty(pte) && pte_write(pte))
+                        pte_val(pte) &= ~PTE_RDONLY;
+                else
+                        pte_val(pte) |= PTE_RDONLY;
         }
 
         set_pte(ptep, pte);
@@ -376,7 +378,7 @@ static inline pmd_t *pmd_offset(pud_t *pud, unsigned long addr)
 static inline pte_t pte_modify(pte_t pte, pgprot_t newprot)
 {
         const pteval_t mask = PTE_USER | PTE_PXN | PTE_UXN | PTE_RDONLY |
-                              PTE_PROT_NONE | PTE_VALID;
+                              PTE_PROT_NONE | PTE_VALID | PTE_WRITE;
         pte_val(pte) = (pte_val(pte) & ~mask) | (pgprot_val(newprot) & mask);
         return pte;
 }